Systems and methods for biomass digestion

ABSTRACT

Provided herein are systems and methods for biomass digestion and products formed thereof. The products include one or more biogases, U.S. Environmental Protection Agency classified Class A Biosolids, and pathogen reduced organic liquid fertilizer. Through the digestion of waste materials using sequential phases in an efficient digestion process, enhanced biomass conversion efficiency and improved output of products (in quantity and/or quality) are obtained with a significant reduction in dwell time in each phase.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/346,368 filed Jan. 9, 2012, which claims priority to and is acontinuation of U.S. patent application Ser. No. 12/258,925 filed Oct.27, 2008, which claims the benefit for priority of U.S. ProvisionalApplication No. 60/982,672 filed Oct. 25, 2007, and U.S. ProvisionalApplication No. 61/078,835 filed Jul. 8, 2008, all of which areincorporated herein by reference in their entirety for all purposes.

BACKGROUND

Waste material may include material obtained from waste streams, such assewage, sewage sludge, chemical wastes, food processing wastes,agricultural wastes, animal wastes including manure, and other organicwaste and materials. Waste materials, collectively referred to herein asbiomass, when broken down, may be used as a source of hydrocarbon, suchas methane and/or other biogases, biosolids and other biofuels orbioproducts. Waste materials may also serve as a source of organicfertilizer. Unfortunately, processes to produce hydrocarbons, such asmethane and/or other bioproducts or biofuels (e.g., biogases, biosolids,safe fertilizers, biosupplements) are complicated, costly and difficultto control.

SUMMARY

As described, the invention relates generally to the field of anaerobicdigestion of biomasses. More particularly, the present invention relatesto the conversion of biomass to methane or other bioproducts orbiofuels, such as biogases, biosolids, safe fertilizers, and biosupplements.

In various embodiments are provided one or more processes, apparatus,and systems for production of output that includes one or more biofuelsor bioproducts (e.g., biogases, biosolids, fertilizer and/orbiosupplements). Said output is provided by waste/biomass input into oneor more digesters, generally via a feed stream. Such biofuels orbioproducts are produced via digestion of said waste materials, asfurther described herein. Said digester systems as described herein mayyield a high biomass conversion efficiency at a high conversion rate.Conversions by digester systems described herein produce one or morebioproducts and biofuels, such as decomposed solids and biogases. In oneform, a produced biofuel or bioproduct complies with a U.S.Environmental Protection Agency (EPA) classification as a Class ABiosolids. In addition or as an alternative, a produced biofuel orbioproduct includes one or more biogases, such as methane and hydrogen.In addition or as an alternative, a produced biofuel or bioproductincludes a safe and organic liquid fertilizer, a pathogen reducedfertilizer and/or a pathogen reduced biosupplement.

In one or more embodiments biomass digesters described herein areprovided with increased efficiency that may enable reductions indigester volume and/or reactor size. In turn, such reductions shouldlead to reduced capital costs and reduced energy requirements, as aconsequence of lower heating and mixing demands, as examples.

As described herein, in one or more forms, operating efficiency may beenhanced by a separation of phases in the digestion process, whereineach phase is identified as an isolated stage. Separation enablesindependent environments that may be pre-selected and optimized for eachphase that includes a specific group of microorganisms involved indigestion. Separation of stages allows independent manipulation of agiven stage in order to enhance production of a particular output, suchone biogas over another or the co-production of one or more outputproducts. Separation also allows one or more microbial environments tobe independently manipulated for activity, inactivity and/or growth. Forexample, effective isolation of acidogenic microbes helps manage theirnormally very rapid and aggressive growth. Together, the independence ofphase environments and separate control of said phases provides a morestable operation by minimizing process upsets (e.g., microbedisplacement and spillover that could normally be caused by unequalmicrobial growth) and provides uninterrupted operating periods thatshould maximize biogas, biosolid and/or biofuel production.

In one or more embodiments, systems and processes described herein mayprovide stable anaerobic digestion and uninterrupted plant operationwith reduced plant upsets, upsets that are normally due to unequalgrowth rates of one or more microorganism. Hence, described herein is ameans for efficient manipulation of one or more desired microorganismsand their activity within a given and isolated phase.

In yet other forms, systems and processes described herein may providegreater production of desired digestion products due to, in part, todecreased plant delays, interruptions and more efficient processing ofwaste/biomass.

Additional embodiments, as described herein, may include systems andprocesses for treatment and recycling of biomass water and effluent usedin the digestion process. Such treatment reduces the overall amount ofwater consumed in digestion processes, as described herein.

Still further embodiments described herein include more manageableenvironmental conditions for microorganisms, including more moderate pHfor microbe preservation, avoidance of over-acidification as well asminimal operating energy requirements, particularly suitable forcommercial applications. Such enhancements promote system efficiency andstability.

In many embodiments, systems and processes described herein may provideefficient and on-demand biomass digestion and output production withouta need for regular biomass biosupplements. Enhanced efficiency, asdescribed herein, allows for digestion and output production withminimal operating energy requirements. Enhanced efficiency also providesfor the reliable production of one or more biogases, biofuels and/orbiosolids, including safe organic fertilizer.

Still further, as described herein are provided systems and processesthat may be used for production of one or more biogases, includingmethane and/or hydrogen, wherein said one or more biogas may be used asan energy source for the digester system described herein.

In additional embodiments, described herein are parallel operations oftwo or more digester systems, which may further include the feeding ofmethane from one system into another system. Such parallel operationand/or sharing of resources may promote production of additional methaneand/or other biofuels or bioproducts, such as hydrogen, Class ABiosolids, fertilizers and/or biosupplements, in one or more of thesystems.

Other embodiments described herein may include operation of digestionphases in series, thereby further enhancing biofuel or bioproductproduction from a given feed stream For example, two thermophilicdigester reactors may be positioned in series to enhance and moreefficiently produce methane and/or hydrogen and/or other biogases from afeed stream.

Yet further embodiments, as described herein, may include a consumptionof a portion of volatile solids from a given biomass feed stream forproduction of a biogas, such as, for example, methane and/or hydrogen,with consumption of the remaining portion for production of one or moreother biogases.

One or more embodiments provided herein may include the capability toadjust the amount of volatile solids in one or more portions of the feedstream without increasing water demands in a particular digestion phase,such as the hydrolysis phase.

Those skilled in the art will further appreciate the above-notedfeatures and enhancements together with other important aspects thereofupon reading the detailed description that follows in conjunction withthe drawings.

BRIEF DESCRIPTION OF THE FIGURES

For more complete understanding of the features and advantages of theinventions described herein, reference is now made to a description ofthe invention along with accompanying figures, wherein:

FIGS. 1A, 1B, 1C and 1D are each block diagrams, each schematicallyillustrating a representative system and process of biomass digestion asdescribed herein, including output production of one or more biofuelsand/or bioproducts;

FIGS. 2A and 2B each depict representative side view configurations fora digestion reactor as described herein, which include a representativerecirculation device;

FIG. 3 depicts a representative process for dewatering effluent;

FIGS. 4A and 4B each depict representative schematics for a gas treatingmethod as described herein;

FIG. 5 depicts schematically a representative biogas stripping apparatusas described herein;

FIG. 6 depicts a front cross section of a representative digestionreactor that includes a dissolved air system as described herein;

FIG. 7 depicts an end view of a dissolved air system of FIG. 6incorporated into a digestion reactor;

FIG. 8 illustrates a representative flow chart as described herein forproducing one or more biogases, including methane;

FIG. 9 illustrates a representative flow chart as described herein forproducing one or more biosolids, biofuels and/or biosupplements,including pathogen reduced liquid fertilizer and pathogen reducedbiofuels and biosupplements;

FIGS. 10A and 10B illustrate a representative flow chart as describedherein for producing one or more biogases, including methane, using twothermophilic reactors in series; and

FIGS. 11A and 11B illustrate together a representative flow chart asdescribed herein for producing one or more biogases, including methane,using two biomass digester systems in parallel.

DETAILED DESCRIPTION

The invention, as described herein, may be better understood byreference to the following detailed description. The description ismeant to be read with reference to the figures contained herein. Thisdetailed description relates to examples of the invented subject matterfor illustrative purposes, and is in no way meant to limit the scope ofthe invention. The specific aspects and embodiments discussed herein aremerely illustrative of ways to make and use the invention, and do notlimit the scope of the invention.

Waste material includes material obtained from waste streams, such assewage, sewage sludge, chemical wastes, food processing wastes,agricultural wastes, animal wastes including manure, and other organicwaste and materials. Waste materials, when digested may provide a highamount of one or more biogases, biosolids, and/or other biofuels andbiosupplements. Waste materials may also serve as a source of organicfertilizer. Unfortunately, processes to produce such output products,including methane and safe fertilizers, are complicated, costly anddifficult to control. For example, cow manure, which may be composted toproduce a safe fertilizer, is difficult to process and is costly toprocess. The unreliability in current composting methods are evidencedby recent outbreaks of one or more pathogen infections in humans, suchas Escherichia coli infection after the ingestion of spinach and lettucethat had been organically fertilized and irrigated with composted cowmanure. The E. coli outbreak prompted product recalls, caused numerousinfections, and even resulted in death. Pathogens that may be present inanimal manure include E. coli, Salmonella typhimurium, Streptococcuspyogenes, and Staphylococcus aureus, to name a few.

Digestion processes have been used to treat and remove organic compoundsfrom waste streams containing the above-mentioned waste material (alsoreferred to herein as biomass). Biological anaerobic digestion ofbiomass wastes produce, in one form, methane. Conventionally, naturalgas, which is about 95 percent methane, is mined from deep natural gasdeposits, which is very costly. The biologic digestion process reducescarbon dioxide emissions and does not require expansive mining projectsor destruction of natural resources.

Unfortunately, current biomass digestion systems are large and costly tobuild. For example, the size of a conventional digester is 15 to 20times the daily waste volume. In addition, such a digester requires highlevel management. A biomass digester for methane production andelimination of volatile solids may also be susceptible to environmentalchanges and a biological upset may take months to correct. And, with adigester system upset, methane generation and volatile solid reductionmay decrease dramatically or even stop. As of yet, digester systems andbiomass methane generation are not viable energy options for commercialand/or farm use. The same can be said that there are currently no viablemeans for providing risk-free commercial grade fertilizer using biomassdigester systems.

Generally, biomass for digestion is placed in a feed stream and isdiluted, or otherwise adjusted, to achieve a desired solution ofsuspended solids. Most conventional standard multi-stage anaerobicdigestion systems include two phases, an acidogenesis phase and amethanogenesis phase, each of which are physically separated. Theacidogenesis stage may or may not be combined with a hydrolysis stage.Acidogenesis, as a separate stage or combined with hydrolysis, precedesthe methanogenesis stage. Typically, heat is added to the acidogenicphase but not in the methanogenic phase. The methanogenesis stage may befurther preceded by a thermophilic stage; however, this stage isuncommon because it involves digestion by thermophilic microbes thatconvert acid chains to methane and is a much more volatile process thanmesophilic methanogenesis (which uses mesophilic microbes). Thermophilicmethanogenesis, when present, may be separated from mesophilicmethanogenesis. Such stages may be separated by temperature.

While some current systems may separate some phases, such as hydrolysis,into one or more stages (e.g., a hydrolysis phase may be separated intothree stages using escalating temperatures), such systems and methodsrequire a substantial amount of energy for heating (e.g., for heatingthe final stages of hydrolysis) and one or more essential microbes maybe destroyed at temperatures currently used by these alternativesystems. For example, some alternative system will combine hydrolysisand acidification and hydrolysis enzymes will be included in thecombined phase yet acidic pH levels will result. Too low of a pH,however, may lead to over acidification. In addition, a very low pH maylend to there being a difficulty in controlling pH in one or moresubsequent stages and a very low pH has been known to attenuate growthof methanogenic microbes.

In one alternative multistage anaerobic digester, a partiallypartitioned long rectangular container was used (e.g., U.S. Pat. No.5,525,229). A modified plug flow with a fixed film reactor was employed.Hydrolysis was separated at the entry chamber of the horizontalrectangular container, continuing to a second chamber for thethermophilic phase and a mesophilic phase was in the third chamber. Theoperating temperatures and pH were the same for the hydrolysis stage andthe thermophilic stage. Unfortunately, such conditions are not found tobe conducive for timely acidogenesis and biogas production. Sufficientand timely acidogenesis are needed to enhance biomass digestion andmethane/biogas generation rate.

A biofilm that increases surface area for bacterial growth may appear indigestion processes and will also add to maintenance demands of adigestion system. Biofilm production has been a problem particularly insystems in which all multi-stage chambers are in fluid communicationwith each other, such as that of U.S. Pat. No. 5,525,229. Spillover isalso a problem in such a design as that of U.S. Pat. No. 5,525,229.

As described herein, systems, methods, and apparatus are provided thatovercome many shortcomings of other biomass digesters. Digestersdescribed herein are capable of accommodating a large variety of organicwaste. An improvement included herewith is increased digester efficiency(e.g., lower heating and mixing demands) that can translate intodecreased digester volume and/or reactor capacity/size, reduced energyrequirements during operation and cost savings.

Operating efficiency is enhanced with systems and processes describedherein via a number of avenues, including separation of phases duringdigestion, providing uninterrupted operating periods as well as energyand water reductions. Generally, digesters as described herein includefour separate stages, such that there may be a unique and independentsetting for each group of microorganisms specific to each digestionstage, including hydrolysis, acidogenesis and methanogenesis, includingat least one thermophilic and mesophilic phase. Feed stream is movedbetween each separate stage by means of one or more pumps, pipelines andcontrol valves. A feed stream as described herein may include a biomasswith or without additional water, an output after digestion and/orbetween digestion stages, within one or more digestion stages or outputfrom one or more digestion stages. As further described, systems andmethods herein improve overall biomass digestion, enhance generationrate of methane and/or hydrogen and output of safe organic liquidfertilizer, Class A Biosolids and other pathogen reduced fertilizersand/or biosupplements. Separate phase environments allow for optimumconditions of microbe activity and growth and minimizes digestionprocess upsets that would ordinarily occur with microbe displacement andspillover and/or unequal microorganism growth rates. When, in otheralternative systems, microbes spill over, production is generally haltedand efficiency may be significantly reduced because water and energyusage cannot be effectively managed. On the other hand, more manageableand moderate reactor conditions as described herein (e.g., pH and/ortemperature), preserve microbe colonies and minimize energyrequirements, both of which are particularly suitable for commercialapplications.

As described herein, treatment of and recycling of water is used, whichtranslates into a reduced amount of water consumed with the digestionprocess.

Still further is provided a method and system whereby methane productionis sufficient to meet the energy requirements of the digester.

Referring now to FIGS. 1A-1D, representative diagrams of digestionprocesses and components, as further described herein, are shown, whichinclude at least one hydrolysis phase 1, at least one acidic phase 2, atleast one thermophilic phase 3 and at least one mesophilic phase 4.Generally, waste (block 1A) and optionally water (block 1B) are fed viaa feed stream to hydrolysis phase 1. In some embodiments, waste (alsoreferred to herein as organic waste and/or biomass feed) is diluted witha specified volume of water to provide a desired solids content. Inaddition or as an alternative, waste or biomass is pretreated to providea predetermined solids content. In some embodiments, the solids contentis pretreated to have at or about 15% solids. In addition or as analternative, the solids content may be at or about 12% or less, or about10% or less, or about 7% or less. The solids content may span a range offrom about 1% to 15%, or from about 1% to 7% or from about 4% to 7%, orfrom about 6% to 7% or from about 7% to 15% or from about 7% to 12% orfrom about 10% to 12%. In yet another embodiment, the total suspendedsolids content may be reduced to at or about 2% to 3%, facilitatingproduction of one or more select biogases in the thermophilic phase. Alow solids content in one embodiment may be combined with a higher totalsuspended solids content in a parallel system, in which one system ismore favorable to production of one biogas and the other system is morefavorable to production of a second biogas. In still furtherembodiments, at least two biomass digesters are operated in parallel,wherein one digester has a pretreated feed stream yielding a 2% to 4%total solid suspension and a second pretreated feed stream yielding ahigher percent of total suspended solids, for example, greater than 4%or at or about 5% to 15% total suspended solids or about 6% to 7%, or aneven greater percentage of solids. Pretreatment may involve dilution,dehydration, screening and/or emulsification to achieve the desiredsolids concentration. Often, pretreatment may be determined by theactual contents/components of the waste, as is known and understood byone skilled in the relevant art. Pretreatment of waste may beaccompanied by additional water dilution, when appropriate or desired.

In the hydrolysis phase (block 1), which is an aerobic phase, the feedstream is typically maintained at a temperature suitable for hydrolysis,often at an optimal temperature. Generally, the temperature is at orless than about 80° F. or 85° F. Often, the temperature is between about60° to 85° F. Biomass remains in the hydrolysis phase for a period ofabout 12 hours to up to about 36 hours.

In some embodiments, the hydrolysis phase includes a pretreatment stage,as previously described above. As such, pretreatment and hydrolysis maybe performed in the same reactor or in alternate vessels. In someembodiments, for example when pretreatment and hydrolysis stages arecombined, dwell time may be for as long as 36 hours. In alternativeembodiments, said dwell times may be for as long as 28 hours or as longas 24 hours or as long as 20 hours.

Generally, mixing of the feed stream occurs initially in the hydrolysisphase. The aerobic atmosphere during hydrolysis encourages faster growthof acidogenic microbes and lends to a stabilization in the consistencyand/or viscosity of the feed stream.

During hydrolysis, complex biomolecules, such as proteins, cellulose,lipids, and other complex organics are broken down into simplermolecules, often in the form of monomers, using water to split chemicalbonds. With acidogenesis, a group of microorganisms begin feeding on themonomers and/or long chain fatty acids obtained from the hydrolysisstage. Acidogenic microorganisms produce volatile fatty acids. In thethermophilic stage, when present, a group of microorganisms produceacetic acid, carbon dioxide, oxygen, and methane from volatile fattyacids. In addition, thermophilic microorganisms produce acetic acidintermediates, including propionate and butyrate, as well as hydrogenand carbon dioxide. Because digestion by thermophilic microbes is morevolatile, this stage is often excluded in conventional digester systems.

During the methanogenic stage, a group of microorganisms produce methaneand other products comprised in biogas from the remaining long chainacids and from acetic acid products of thermophilic digestion. Biogasproduced by biomass digestion typically comprises about 55-70% methane,about 25-30% carbon dioxide, and any remaining mixture includes any ofnitrogen, hydrogen, and hydrogen sulfide. About 70% of methanogenesisincludes a fermentation process in which amino acids and sugars areconverted to acetate; a specific group of microorganisms in thethermophilic stage convert acetate to methane. Up to 30% ofmethanogenesis may be a redox process, using hydrogenotrophic microbesthat oxidize hydrogen with carbon dioxide (the electron receptor) toproduce methane and thermophilic synotroph microbes that oxidize acetateto form hydrogen and carbon dioxide.

Referring again to FIGS. 1A-1D, a feed stream from block 1 moves toblock 2, the acidic phase. Transport from hydrolysis phase to acidicphase occurs when a desired retention time in the hydrolysis phase hasbeen reached. A reaction vessel for the acidic phase is constantly fedat a volatile solids loading rate that is a function of the individualfeed stream used for a particular waste and digestion process. In someembodiments, a feed stream is heated prior to entering the acidic phase.In this manner, one or more feed stream heat sources are placed betweenseparate vessels and temperature is adjusted by passing a feed streamthrough a heating element or heat source that controls temperature, suchas a heat exchanger or heating pad (as depicted in block 2A). Inaddition or as an alternative, a hydrolysis vessel may include anexternal or internal heat source, such as heat exchanger or heating pad.

The acidic phase is generally held at an elevated temperature that ishigher than that of the hydrolysis phase. In some embodiments, thetemperature in the acidic phase is less than 100 degrees F. Thetemperature may often be between about 95° and 100° F. or between about95° and 98° F. The pH in the acidic phase is generally below about 6.5.The pH in the acidic phase may be between about 5.8 and 6.2. Theretention time of the feed stream in the reaction vessel foracidogenesis may be about 12 to 24 or about 12 to 20 hours. In someembodiments, the retention may be about 16 hours. In additionalembodiments, the retention may be 16 hours. It has generally been foundthat as dwell time approaches or exceeds about 24 hours, overacidification may occur and the control of pH may become problematic.Conditions in the acidic phase are anaerobic. Generally, conditionsafter the hydrolysis phase are anaerobic.

Generally, at least one airtight vessel is used for each anaerobic phaseto provide independent conditions and encourage a desired microbialactivity. In the acidic phase, acidogenic anaerobic microbes break downthe contents in the feed stream into short chain acids and producecarbon dioxide.

In several embodiments described herein, anaerobic conditions during anyanaerobic digestion phase are improved by a recirculation of anaerobicgases, such as carbon dioxide, as shown in line 2C, lines 3C and lines4C (FIGS. 1A-1D). Any gas fluid mixing systems may be used forrecirculating anaerobic gases. For example, carbon dioxide produced byacidic microbes in the acidic phase may be removed via a product line(block 2B) and may also be recirculated (line 2C) to maintain anenvironment that is anaerobic, so as to maintain little to no oxygen inthe vessel. In addition or as an alternative, any of the digestervessels may employ a mixing and/or blending system in which one or moregases, such as carbon dioxide or a biogas, is recirculated by removingsaid gas or gases above the fluid line and then injecting the gasesthrough an inlet in the tank, often at the bottom or side of the tank. Abubbling device, such as that taught in U.S. Pat. No. 4,595,296, mayalso be used, which provides bubbles of a predetermined and/or ofvariable size at one or more frequencies. With U.S. Pat. No. 4,595,296,gas is injected via an inlet. As described herein, one or more gases maybe introduced into a reaction vessel through one or more air inletopenings with or without an accumulator plate. Inlet orientation may bepredetermined and may include either a single inlet or a ring of two ormore inlets (that may further include and encircle a center inlet) atany desired position. Via placement of inlets, circular and/or toroidalgas flows may be created in the contents of the tank or vessel. In oneor more embodiments, placement may be at or near the bottom of thevessel. In addition or as an alternative, placement may be at the topand/or at the sides of the vessel. In addition or as an alternative,placement may be at or near the middle of the vessel. Other bubblingand/or mixing methods may also be used in combination with arecirculating system, including inlets that have crossed pipes withholes in them and/or a gas lift mixing device that may have an eductortube and/or an accumulator plate (see FIGS. 2A, 2B). Still further fluidmixing systems, such as motors, jets and/or diffusers may be used formixing the contents of a vessel, used alone or in combination with arecirculating system as described herein.

In addition, a mixing system may be included to advance digestion morequickly. In one or more embodiments, a gas, such as carbon dioxide orother air or gaseous mixture may be pumped through a device, such as amixing device or via one or more jets or diffusers, to keep the feedstream in a state of suspension. The mixing generally provides abubbling in the mixture and the bubbling enhances microbial growth, asbubbles feed in and around microbes for optimum microbial activity andgas generation. In addition or as an alternative, the mixing device mayalso generate a stable mixing pattern to keep the contents in a stablesuspension. The gas, such as carbon dioxide or other air mixture, alsoprovides a blanket on the surface of the biomass during the acidic phase(e.g., the gas collection zone or freeboard section) and may be used todisplace oxygen away from the microbes.

Gas recirculation and/or auxiliary mixing in a reaction vessel willgenerally occur with each anaerobic phase (e.g., acidic, thermophilic,mesophilic) as depicted in FIGS. 1A-1D, and, as described herein, offeradditional benefits, including a reduction in thermal stratification anda dispersion of volatile biosolids, which increases their contact with amicrobe and their subsequent breakdown. By maintaining the biomass insuspension and in combination with a continuous and/or desired feedrate, conditions for digestion are maximized, which promotes morecomplete digestion and significantly reduces emission or output ofnon-digested products from the system.

Auxiliary mixing methods that may be used include low energy air mixing(continuous and or discontinuous), pump and jet mixing, a gas liftmixing, mechanical mixing, and/or hydraulic mixing.

While other conventional systems and processes often combine the acidicstage with the methanogenesis stage, the problem is that such systemswhen combining these stages are subject to a higher concentration ofcarbon dioxide in the biogas produced therefrom. As described herein,the separation of an acidic stage from a phase for biogas and methaneproduction reduces the concentration of carbon dioxide in the biogasproduced therefrom, thereby reducing contaminants in the biogas.

Referring again to FIGS. 1A-1D, after completion of the acidic phase(block 2), the feed stream is transported to a next segment ofdigestion, which is the thermophilic phase (block 3). In one or moreembodiments, transportation of the feed stream to this next stage is bypump. Because thermophilic microbes are active in a less acidicenvironment, the pH is higher in the thermophilic reactor vessel.Generally, the pH is at about 7.5 or less. The pH may be in a range of6.8 to 7.2. In one or more embodiments, pH is modified between one ormore reactors by a pH adjustment system, such as that depicted in block9. Such an adjustment system generally shocks or rather quickly adjustspH in the feed stream when it is between digestion stages or when thefeed stream is within a digestion vessel. In one or more embodiments, atleast one pH adjustment system may be located between an acidic stageand a thermophilic stage. In addition or as an alternative, at least onepH adjustment system may be located between a thermophilic stage and amesophilic stage. As desired or appropriate, a pH adjustment system maybe associate with any of the additional reactors in the digestionsystem. A pH adjustment system is operable to adjust the pH of the feedstream in at least one location that includes the feed stream beforeentering the at least one anaerobic vessel, the feed stream in the atleast one anaerobic vessel, and the feed stream after leaving the atleast one anaerobic vessel. In one example of an adjustment system, pHis modified by addition or injection of a chemical, such as sodiumbicarbonate. Sodium bicarbonate (or similar chemical) injection will addadditional carbon atoms to the feed stream and increase methane contentin the biogas generated therefrom. In addition or as an alternative, pHis adjusted using alternate methods, including addition or injection oforganic bases, such as calcium carbonate, calcium oxide, calciumhydroxide, magnesium hydroxide, sodium hydroxide, aluminum hydroxide,and dihydroxyaluminum sodium carbonate, as examples. pH in thethermophilic vessels may be continually monitored and controlled byinstrumentation and by additional injection of one or more basiccompounds. Gas injection in any of the reaction vessels includes a gasinjection line with one or more control valves for injecting a gas intoa feed stream. Chemical injection may include a similar line or aseparate line with valves for controlling input. Gas and/or chemicallines may feed into a reaction vessel or prior to feed stream entry intothe vessel.

The pH and temperature changes will curtail the acidogenesis reaction,diminish the population of acid microbes in the feed stream, retardgrowth of any surviving acid microbes, and stabilize the feed stream,particularly as it enters the thermophilic stage.

Temperature in the thermophilic phase is increased by passing the feedstream through a heating element, such as a heat exchanger (block 3A) orby heating the feed stream in the thermophilic reaction vessel.Generally, the heating element of 2A and of 3A are separate elements. Inone form, a single element is used to heat and cool effluent, whereinthe shell side of a conventional heat exchanger can heat effluentpassing there-through, and the tube side of the heat exchanger can cooleffluent received from a second source. In another embodiment, the sameelement heats the post acidic phase effluent and cools the postthermophilic phase effluent via respective tube and shell sides. Inanother embodiment heat of a pre-acidogenic feed stream and apost-thermophilic feed stream are achieved through the same element.While in further embodiments as depicted in FIGS. 1A-1D, separate heatelements are used between each phase and/or between each vessel.Accordingly, the number of said elements may be varied while stillkeeping with the spirit of the invention, such that a single element orheat exchange system may be utilized in each of the embodimentsschematically depicted in FIGS. 1A-1D.

The thermophilic reactor is a constantly mixed reactor. The vessel maybe a single vessel. As an alternative, the thermophilic phase maycomprise multiple vessels, as well as vessels in series or in parallel,as depicted in FIGS. 1C and 1D, respectively. In addition, or as analternative, a mixing device as previously described may also beincluded with one or more of the thermophilic vessels. Mixing keeps thefeed stream in suspension and prevents solids from settling into asludge layer. Operating parameters in the thermophilic phase areindependent and may be adjusted to provide an optimum environment forremaining acetogenic and methanogenic microbes that cohabitate in thevessel. Cohabitation promotes efficient biogas production and volatilesolid digestion in the anaerobic digestion process into decomposedsolids. Operating parameters for the thermophilic phase generallyinclude a more elevated temperature than that of the acidic phase.Typically, the temperature in the thermophilic phase is less than about150° F. In many embodiments, the temperature is in a range from about125° to about 140° F. In an alternate embodiment, the temperature rangesfrom about 130° to about 140° F.

The retention time of the feed stream in the thermophilic stage is fromabout 24 to 96 hours. In alternative embodiments, the retention time maybe from about 24 to about 28 hours. In still other embodiments, thedwell time is from about 30 to 35 hours. To reduce energy demands, thedwell time may be kept to 48 hours or less. A higher temperature willgenerally reduce the dwell time. For example, in one embodiment tomaximize methane production efficiency, the retention time is 31 hourswith a temperature of 130° or 131° F. In yet another embodiment, thetemperature of the thermophilic stage is as high as 160° F. while thedwell time is reduced in order to achieve Class A Biosolids (block 14)and fertilizer and/or biosupplements (block 13). And, in yet anotherembodiment, with a temperature of 125° F., the dwell time for producingClass A Biosolids and fertilizer and/or biosupplements (block 13)approaches 3 days.

As with previous phases, the one or more vessels of the thermophilicphase are generally fed at a volatile solid loading rate. The feed rateis typically constant and the rate a function of the biomass contents.In one or more embodiments, the feed rate may be up to 2.66 lb/ft³.Other feed rates, may also be used. Said feed rates generally depend onone or more implementations as described herein. For example, systemsand processes described herein may handle higher feed rates thatalternative systems, due in part to one or more adjustment systemsincluded herein, such as a dissolved oxygen adjustment system and a pHadjustment system.

The thermophilic phase begins the initial production of biogas (block11, FIGS. 1A-1B and block 16, FIGS. 1C and 1D). Biogas or at least aportion thereof produced in this phase of the process is generallyrouted to one or more treating phases (block 10, FIGS. 1A-1B; blocks 10Aand 10B, FIGS. 1C-1D) via a pipeline and one or more control valves. Thebiogas produced is generally a mixture of gases. The treating phaseseparates and/or purifies the one or more gases from the biogas mixture.Recirculating lines 3C may be included to recirculate a partial streamof the produced biogas back through the thermophilic vessel. Similarly,as depicted in FIGS. 1A-1D, recirculation may also occur with themesophilic phase, as described further below.

In one or more embodiments, recirculation includes a gas recirculatingline with one or more control valves routed via a recirculationcompressor or blower. Recirculation may be in combination with a mixingdevice, such as a gas lifting mixing device, as previously described, orany alternate mixing system, alone or in combination. The mixing systemensures that contents in each reactor, such as the thermophilic reactor,are thoroughly mixed and in suspension. Mixing action may also produce abubbling condition that contributes to a hospitable environment forthermophilic microbes to inhabit. Recirculated biogas also provides agas blanket on the surface to displace oxygen and maintain an anaerobicatmosphere.

Recirculation of a biogas may operate in parallel with a dissolved airsystem, as described below and as shown in a system of FIG. 1C. Thecombination allows for a partial oxidation of methane to methanol, whichis a source of feed for select microbes, such as hydrogen producingmicrobes. In addition or as an alternative, methanol may be fed in to athermophilic reactor in the absence of biogas recirculation, such as ina system shown with FIG. 1A. In such an example, additional parameterswill likewise be adjusted to suit production of one or more biogases,such as that of hydrogen. In still another embodiment, biogas from amesophilic reactor may be fed into either a thermophilic vessel (e.g.,block 3 as depicted in FIG. 1A) or into a second thermophilic reactor(e.g., block 3D as depicted in FIG. 1C) which provides for subsequentoxidization of methane into methanol. When running a parallel systemembodiment, such as one shown in FIG. 1D, biogas from a mesophilicvessel provided with a low feed stream may also be fed into athermophilic reactor (also provided with a low feed stream) to promotehydrogen production.

The thermophilic phase at the dwell time and temperature levelsdescribed herein yield Class A Biosolids (see, e.g., Alternate Flow,lines 19, FIGS. 1B and 1C, and may also occur with FIG. 1D, though linesnot shown), including biosolids that meet standards of the EPA (e.g.,see 40 C.F.R. §530). In addition, the thermophilic phase conditionsdescribed herein kill pathogens in the feed stream, which assist in theclassification of such biosolids as Class A Biosolids (block 14) and inproduction of a pathogen reduced organic liquid fertilizer and/or otherpathogen reduced fertilizer and/or biosupplements (block 13, FIGS.1A-1D).

As described herein, in one form is a digester that includes amulti-phased, multi-stage, process that maintains an independentmicrobial environment within each phase of the digestion process.Independent environments allow for optimization of conditions forenhanced production of one or more desired end products. A separatestage for acidogenic microbes, such as E. coli, L. mesenteroides, and C.butyricum and others, is preferred because acidic microbes need aslightly acidic pH and a temperature just below human body temperaturein order to thrive with rapid growth and consume the biomass feedstream. Acid microbes are aggressive in their growth and propagation. Incontrast, methane producing microbes, such as M. bakeri, M. bryantii andM. formicicum, that are slower growing and need an independent stage foroptimal growth so that acid microbes, which manifest rapid aggressivegrowth, will not displace the slower growing methane and syntropicmicrobes, particularly if acid microbes are commingled with the latter.

Biochemical oxygen demand (BOD) and chemical oxygen demand (COD) may bemonitored and controlled during the digestion process described herein.Monitoring and adjusting of BOD level, which is an assessment of thedifference between an initial and a final dissolved oxygen level, helpspromote efficient operating parameters. BOD and COD are both essentiallya measure of oxygen level, and when in decline may be indicative of areduction in a desired microbe population that consumes dissolved oxygenin that reaction. Swings or fluctuations in BOD measurements may signalan impending plant upset. A rise in ammonia content is also associatedwith a high BOD and COD and is generally detrimental to the operatingstability of the digestion system. On the other hand, some embodimentsmay desire a slightly elevated ammonia amount, particularly thosesystems that operate digestion phases in parallel (e.g., FIG. 1D) and/orwhen methane oxidation is preferable because ammonia acts as a catalystfor oxidation of methane. For example, a higher ammonia content, in someembodiments, such as those having a second thermophilic reactor, isdesirable because ammonia acts a catalyst for oxidation of methane tomethanol.

High BOD and COD measurements may be adjusted for by use of a separateadjustment system, which may include addition of dissolved air oroxygen. Generally one or more COD measurements are made and converted toadjust the BOD level in a reaction vessel. As referred to herein, adissolved air adjustment system (or DAS) circulates (and mayrecirculate) oxygen or air as a means for controlling BOD. Oxygenadjustment is generally made in either or both of the thermophilic andmesophilic stages. In one or more embodiments, oxygen adjustment isprovided by a dissolved air system installed in at least one of athermophilic and/or mesophilic reactor, as depicted schematically inFIG. 6, which illustrates a front cross section of a representativereaction vessel 600 that includes a DAS for BOD and COD control.

A dissolved air system as represented in FIG. 6, includes generally apump 610, which is typically a recirculation pump, a suction line 620,and a venturi type assembly 630 in a discharge line 640 for infusing airinto a feed stream 650, which raises dissolved oxygen level in the feedstream which feeds into vessel 600. Feed stream, in one form, may movethrough the suction line followed by air or oxygen infusion and re-entryinto the vessel. Raising dissolved oxygen levels, when appropriate, willenhance the digestion environment for microbes. Addition of dissolvedoxygen or air in this manner does not disturb a desired anaerobicenvironment in the vessel, because free air or free oxygen is notgenerally introduced into the reaction vessel, itself, but into the feedstream prior to entry into the vessel. In addition or as an alternative,ozone may be fed into the venturi port to supply an even higher level ofdissolved oxygen into the feed stream. In other embodiments, an airdiffuser with a compressor may be used to provide dissolved air into afeed stream or directly into a reaction vessel via lines.

Referring again to FIGS. 1A-1D, from the thermophilic reactor, thebiomass feed stream is transported by a pump and pipeline and mayoptionally pass through a heating/cooling element, such as a heatexchanger (blocks 4A and 4B), to the mesophilic phase (block 4). Again,heating elements, as depicted in FIGS. 1A-1D, may be replaced or beassisted by one or more external or internal vessel heating sources usedto heat the vessel content and/or for heat maintenance. The design may,in many instances, depend on reactor size. In one or more embodiments,transport from one reactor, such as thermophilic reactor, to the nextoccurs after a desired retention time is reached at the exiting end ofthermophilic reaction vessel.

The mesophilic phase of the process is a second phase of biogasgeneration, depicted as block 11 and/or block 16. The vessel(s) usedwith the mesophilic phase are generally constantly fed at a loading ratethat is a function of the individual biomass feed streams used in theprocess. For the mesophilic phase, a different set of operatingparameters are generally used as compared with those of the thermophilicphase. The mesophilic stage is generally cooler than the thermophilicstage. In one or more embodiments, the feed stream is cooled beforeentry into the mesophilic phase. For example, as described herein, thetemperature in the mesophilic stage is generally about or less than 100°F. In many embodiments, the temperature is in a range of between about94° F. and about 100° F. In some embodiments, the temperature is at orabout 95° F.

pH in the mesophilic phase is typically less than about 7.5. In severalembodiments, the pH is from about 6.8 to 7.2. Retention time isgenerally from about 95 to about 170 hours. Often, the retention time isbetween about 100 to 115 hours. In one or more embodiment, thetemperature of the mesophilic phase is 95° F. with a hydraulic retentiontime of 108 hours. It has been found that too low a retention (e.g.,less than about 95 hours) may reduce the maximal amount of biogascapable of being achieved. On the other hand, too high a retention time(e.g., greater than about 170 hours) will also reduce biogas production.In some embodiments, however, maximal biogas production may not berequired or desired, possibly because biogas supply is in surplus, inwhich case retention time may be prolonged and/or biomass feed streammay be slowed down.

Control and monitoring of pH takes place by inclusion of an adjustmentsystem, similar to that described with adjustment of pH for thethermophilic phase, as depicted in block 9 of FIGS. 1A-1D. The samephysical adjustment system may be used with pipelines leading to bothphases. In other embodiments, a separate system with independentcomponents may be used. In one or more forms, pH is adjusted via asodium bicarbonate injection system, similar to that previouslydescribed. In addition or as an alternative, pH is adjusted usingalternate methods, including injection of one or more chemicals, such asorganic bases, including but not limited to calcium carbonate, calciumoxide, calcium hydroxide, magnesium hydroxide, sodium hydroxide,aluminum hydroxide, and dihydroxyaluminum sodium carbonate, as examples.pH in the thermophilic vessels may be continually monitored andcontrolled by instrumentation and by additional injection of one or morebasic compounds.

As with the thermophilic phase, biogas produced during the mesophilicphase may be routed via a pipeline (generally with control valves) to atreating phase (block 10, FIGS. 1A-1B or blocks 10A and 10B, FIGS.1C-1D). In addition or as an alternative, the biogas or a portionthereof of the gas stream may be recirculated (via recirculating lines3C). Some recirculation is typical and generally involves a separatepipeline and compressor to recirculate some gas back into the mesophilicreactor, the thermophilic reactor and/or the feed stream (see FIGS. 1Cand 1D).

Recirculation in the mesophilic phase includes the use of one or more ofthe mixing devices described previously, which provide mixing and abubbling action in the mesophilic reaction vessel. Mixing prevents thesettling of solids and prevents stratification which can lead to upsetconditions. Gas recirculation, as described herein, may use gas producedin the particular vessel itself or may introduce an additional gas. Gasmay or may not be compressed and then recirculated. Two representativemixing systems 200 and 202 are depicted in FIGS. 2A and 2B,respectively. FIG. 2A shows a first recirculation type (205), whereinFIG. 2B shows a second type with separate lines for biogas removal (210)and for recirculation of gas into a vessel (220). The area depicted by250 is associated with a preferred sloping of the vessel floor for aidin mixing and the prevention of sludge buildup. In one embodiment abottom surface of a reaction vessel slopes to a center at a 3 to 12ratio.

Systems represented by FIGS. 2A and 2B rely on gas being compressed by acompressor (230) and recirculated into the vessel via at least oneeductor tube 240. In one form, a single eductor tube, which may or maynot be centered within a given vessel, can be used. As an alternative,more than one eductor tube may also be positioned at various pointswithin a tank. Each system, whether that of FIG. 2A or FIG. 2B or othersnot shown in detail but described previously, cause some turbulence andmixing of the feed stream, maintain the feed stream in suspension andmay be included for increased efficiency in biogas production andbiomass digestion.

Referring back to FIGS. 1A-1D, at the completion of the mesophilic phase(block 4), biogas production is generally complete and the feed streamcomprising decomposed solids, after passing through a separation processto remove solids (block 5), is typically referred to as effluent (block6). In some instances, after the thermophilic phase, as shown in FIG.1B, an alternative flow path may direct feed stream effluent from thethermophilic phase to the separation process (block 5) to providebiosolids (block 14) and effluent (block 6). In both flow paths, aneffluent pipeline with one or more control valves route feed stream fromeither reaction vessel to the separator. The effluent stream afterseparation includes media rich in nutrients and minerals that are highlyvalued in soil biosupplementation and in fertilizers (block 13) and theproduction will be described in further detail below.

Referring now to FIG. 1C, the figure illustrates an embodiment in whicha thermophilic phase is run in series. With such an embodiment,conditions in a first thermophilic phase (block 3) differ from that of asecond thermophilic phase (block 3D). Dwell time in the firstthermophilic reactor (block 3) may be between about 1 and 3 days, its pHis generally between about 6.8 and about 7.2 and the temperature is atabout 130 to 135° F., generally less than 135° F. or at or about 131° F.In one or more embodiments, a suitable pH is at or about 6.8. Whensuitable conditions are reached, the feed stream is transferred to asecond thermophilic reactor (block 3D). In the second thermophilicreactor, the pH is lower, generally maintained at 6.8 or less or betweenabout 6.4 to about 6.8 and the temperature is greater than in the firstthermophilic reactor, and is maintained at about 135° F. or more,generally between about 135° F. to 158° F. or 135° F. and 138° F. or atabout 137° F. In one or more embodiments, a suitable pH for a secondthermophilic reactor is at or about 6.4. Conditions in the secondreactor are often selected to favor one or more alternate biogases otherthan methane; however methane is generally produced in both the firstand second thermophilic phases. By first routing the feed stream throughthe first thermophilic reactor, the volume of volatile solids in thefeed stream fed into the second thermophilic reactor should be reducedas volatile solids in the first thermophilic phase are digested.Accordingly, one may readily vary the dwell time in the firstthermophilic reactor in order to adjust the percent volatile solidsentering the second thermophilic reactor, and thereby adjust the totaloutput of biosolids, biosupplements and/or biofuels, as desired. Thebiomass feed stream exiting the second thermophilic reactor is generallyrouted to an element (e.g., heat exchanger) as denoted by block 4B forcooling the feed stream to the appropriate mesophilic temperaturedescribed previously or is routed by an alternate path (see AlternativeFlow, line 19) for transfer to the separation process (block 5).

Referring briefly to FIG. 1D, the figure illustrates an embodiment inwhich two biomass digester systems are operated in parallel. For onesystem, organic waste (block 1A-2) is generally pretreated to contain alow total suspended solids content, for example, at about 2% to about3%, thereby forming a low biomass feed stream. A second system,undergoing an alternative pretreatment, produces a higher totalsuspended solids content and higher feed stream, wherein the solidscontent is greater than 5% or up to 15% or between about 5% to about 6%.Depending on the solids content desired in the second system, the wastemay or may not undergo pretreatment. Generally, hydrolysis and acidicphases in both systems may run at the same operating conditions. In someembodiments, and in order to alter biogas production, the thermophilicphases of each system may run under different operating conditions. Forexample, for the low feed stream, the thermophilic phase (block 3-2) mayoperate at a higher temperature that is more favorable to the productionof biogas B, such as hydrogen (block 16). An example of one operatingcondition for the low feed stream is a temperature of about 137° F. witha pH of between about 6.4 to 6.8 and a dwell time about 31 hours. Thehigher feed stream in the thermophilic phase (block 3-1) may be set tobe more favorable for production of biogas A, such as methane. In thisinstance, the operating conditions for the higher feed stream may be ata temperature of about 131° F. with a pH of between about 6.8 to 7.2 anda dwell time about 31 hours. In addition, some biogas A, which may bemethane, may be fed into the low thermophilic reactor (block 3-2). Inaddition or as an alternative, part of the effluent stream having thehigher solids content (block 3-1) may be fed into the thermophilicreactor with the low solids content (block 3-2).

Biogas obtained from either or both of thermophilic phase and/ormesophilic phase will generally be treated by a treating phase (blocks10, 10A and/or 10B in FIGS. 1A-1D). Treatment removes undesiredimpurities, increasing the percentage of one or more biogases, such asmethane, so that the treated gas approaches or exceeds pipeline qualitynatural gas and/or has little impurities. In addition or as analternative, hydrogen and methane are separated from the obtained biogasand provided at desired qualities and/or quantities. Representativetreatment schemes are depicted in more detail in FIGS. 4A and 4B.Additional treatment processes may include resin or gas columnseparation, as is known to one skilled in the relevant art.

Referring now to FIGS. 4A and 4B, representative or exemplary treatmentsystems are shown to receive a biogas stream and to treat the biogasstream, such as through stripping, to produce or extract one or morebiogases. It should be understood that FIGS. 4A and 4B are onlyrepresentative systems, and other systems may be implemented to receiveand treat a biogas stream to produce one or more desirable biogases.

Referring now to FIG. 4A, an exemplary treatment system is shown thatincludes a compressor 410, a dryer, such as a drying vessel 420, astripping vessel 430, a compressor 440, a stripping vessel 450, and avalve 480. The exemplary treatment system of FIG. 4A receives a biogasstream 405, such as from one or both of a thermophilic reactor, such asa thermophilic vessel, and a mesophilic reactor, such as a mesophilicvessel, and treats the biogas stream to extract both methane andhydrogen. In operation, the biogas stream 405 is received at thecompressor 410, which may be implemented as a pump or other availablecompression system, where the biogas stream 405 undergoes compression.The stream passes through a dryer, such as the drying vessel 420, to drythe biogas stream. After passing through the drying vessel 420, the gaspasses through a stripping vessel 430 where, in one embodiment, an earthmineral such as a chabazite is used to filter or strip the gas stream.The media provided in the stripping vessel 430, i.e., the chabazite inthis embodiment, may also be referred to as a molecular sieve. In otherembodiments, other earth minerals may be used, including different typesof zeolites. The chabazite at the stripping vessel 430 absorbs orremoves carbon dioxide from the gas stream. The gas stream, in oneembodiment, may then be compressed again at the gas compressor 440, andthen provided to the second stripping vessel 450. In certainembodiments, the stripping vessel 450 uses a charcoal or carbonactivated charcoal, to filter the gas stream. In this embodiment, thecarbon activated charcoal in the stripping vessel 450 absorbs methane inthe gas stream such that hydrogen may be directed to block 470 to store,accumulate or provide hydrogen. The methane stored within the carbonactivated charcoal of the stripping vessel 450 may be recovered andsupplied to block 460 through the valve 480, which in one embodiment maybe implemented as a let down valve. In one embodiment, the methane maybe provided by isolating block 470 from the stripping vessel 450, andallowing the compressor 440 to operate to pressurize the carbonactivated charcoal such that the methane may be released, and thenprovided to block 460 through the valve 480. FIG. 4A is representativeof a path that may be used to treat and separate multiple gases from abiogas stream, such as, for example, hydrogen and methane obtained froma thermophilic reactor or thermophilic stage.

Referring now to FIG. 4B, an exemplary treatment system is shown thatincludes the compressor 410, the dryer, such as a drying vessel 420, thestripping vessel 430, the compressor 440, and a stripping vessel 490 togenerate methane at the block 460. The exemplary treatment system ofFIG. 4B receives a biogas stream 405, such as from one or both of athermophilic reactor and a mesophilic reactor, and treats the biogasstream to extract or separate out methane. In operation, the biogasstream 405 is received at the compressor 410, which may be implementedas a pump or other available compression system, where the biogas stream405 undergoes compression. The stream passes through a dryer, such asthe drying vessel 420, to dry the biogas stream, and then to thestripping vessel 430. The stripping vessel 430 includes a media thatfunctions as a stripper, filter or molecular sieve to remove portions ofthe gas stream. In one embodiment, a zeolite, such as a clinoptilolite,is used to filter or strip the gas stream. In other embodiments, otherfilters, strippers and/or earth minerals may be used, includingdifferent types of zeolites. The clinoptilolite at the stripping vessel430 absorbs or removes hydrogen sulfide from the gas stream. The gasstream, in one embodiment, may then be compressed again at the gascompressor 440, and then provided to the second stripping vessel 490. Incertain embodiments, the stripping vessel 490 uses a chabazite, similarto the chabazite used in connection with stripping vessel 430 of FIG.4A, to filter the gas stream by removing carbon dioxide from the gasstream. In this embodiment, the remaining methane is then directed toblock 460 to store, accumulate or provide the methane as desired.

A representative example of a stripping vessel is illustratedschematically in FIG. 5, shown as stripping vessel 500 that includes arelief valve 510, gas inlet 540, gas outlet 520, filter media 530 (e.g.,plastic balls, as an example), media chamber 550, and cover lift 560(e.g., davit arm). Generally, compounds used in the media chamberinclude zeolites or other compounds (activated or otherwise) that removehydrogen sulfide and/or carbon dioxide from a gas stream. In one or moreembodiments, the media housed in the media chamber includes chabazite,clinoptilolite, an activated carbon source and/or activated charcoal, asexamples and provided depending on the phase/extent of purification. Forexample, referring back to FIGS. 4A and 4B, in one form a biogastreating system may include chabazite, provided in the stripping vessel430 of FIG. 4A to remove or absorb carbon dioxide in the gas stream, andactivated charcoal, provided in the stripping vessel 450 to assist withseparating methane and hydrogen. In another example, a biogas treatingsystem may include clinoptilolite, included in stripping vessel 430 ofFIG. 4B to remove or absorb hydrogen sulfide in the gas stream, andchabazite, provided in the stripping vessel 490 to remove carbon dioxidefrom the gas and thereby providing a high quality methane. After atreating phase as described herein, at least one biogas (e.g., biogas460) may be, in certain embodiments, equivalent to or better thanpipeline quality natural gas and/or is of a high purity. In one or moreembodiments, some biogas (e.g., methane) may be regulated via one ormore valves, such as the valve 480 (FIG. 4A).

FIG. 8 illustrates a representative flow chart for producing one or morebiogases, including methane, using a digester system and processes asdescribed herein. A biomass is initially collected and then fed as afeed stream. In one embodiment, it may be fed into a water stream (block805) after which a total suspended solids (TSS) is adjusted to a desiredpercentage (block 810), creating a biomass feed stream. In anotherembodiment, the feed stream may not require adjustment in percentsuspended solids content. The feed stream is aerobically hydrolyzed viaa hydrolysis phase (block 815) before being transferred to an acidifyingstage (block 820). Hydrolysis will occur for a period of time, generallybetween about 12 and about 36 hours, which is followed by transfer to anacidogenic phase (block 825) in an anaerobic environment, generally fora dwell time between about 12 and about 24 hour. In one embodiment, thepH is then adjusted (block 830) and the temperature of the acidifiedfeed stream may be raised thereafter (block 835) before the feed streamis transferred to a thermophilic phase (block 840). In an alternateembodiment, block 835 occurs within the thermophilic reactor (block840). In still another embodiment, block 830 and 835 are performed inparallel. In the thermophilic phase, dwell time may be between about 24to about 96 hours (block 845). Biogases generated during methanogenesis,such as during the thermophilic phase, may be recirculated back into thethermophilic reactor (block 847). After the desired or appropriate dwelltime, post-thermophilic effluent is transferred to the mesophilic phase(block 855) after the temperature is lowered (block 850), whichgenerally occurs prior to transfer. The dwell time in the mesophilicstage (block 860) is generally between about 96 to about 170 hours,during which time, generated biogas may be recirculated (block 862)and/or removed (block 865). Extracted biogas will generally be filtered(block 867) before use via a treating phase, as previously described.

FIG. 9 illustrates a representative flow chart for producing one or morebiosolids, biofuels and/or biosupplements, including pathogen reducedliquid fertilizer and pathogen reduced biosupplements and/or fertilizer.With block 905, in one embodiment, a biomass is fed into a water stream(block 905) and adjusted to a desired percent TSS (block 910), which maybe between about 2% and about 15%. In other embodiments, the feed streamis not adjusted in TSS and suitable for further processing. The feedstream is aerobically hydrolyzed (block 915) for between about 12 andabout 36 hours at a pH between about 5.8 and about 6.2. The feed streamis transferred to an acidifying stage (block 920), whereby pH ismaintained between about 5.8 and about 6.2 during a dwell time betweenabout 12 to about 24 hours (block 925). Upon completion of the acidicphase, the pH of the acidified feed stream is raised to between about6.8 and about 7.2 (block 930). Thereafter, the temperature of the postacidogenic feed stream is raised to a temperature between about 125° andabout 158° F. (block 935). In some embodiments, the post-acidogenic pHadjustment (block 930) and temperature increase (block 935) will beperformed in parallel and prior to transfer to the thermophilic stage(block 940). In other embodiments, block 930 and block 935 occur inseries, as depicted in FIG. 9. As an alternative, block 935 may occur inthe thermophilic reactor (block 945). During thermophilic digestion(block 945), biogas produced therefrom maybe recirculated (block 947)and/or transferred for dewatering (block 946) at which time the effluentis separated into one or more biofuels, such as pathogen reduced liquidfertilizer and/or biosupplements (block 949) and biosolids (block 948).

FIGS. 10A and 10B illustrate a representative flow chart for producingone or more biogases, including methane, using two thermophilic reactorsin series. Referring first to FIG. 10A, in one embodiment, a biomass isfed into a water stream (block 1005) and adjusted to a desired a percentTSS (block 1010), which may be between about 2 and 15 percent. In otherembodiments, the feed stream is not adjusted in TSS and suitable forfurther processing. The feed stream is aerobically hydrolyzed (block1015) before being transferred to an acidifying stage (block 1020).Following acidogenesis (block 1025), the pH of the feed stream is raised(block 1030) and the temperature is raised (block 1035), which may occurin parallel or in series. As an alternative, the temperature may beraised after transfer to the thermophilic stage (block 1040). Moving toFIG. 10B, the heated and pH adjusted feed stream is digested in a firstthermophilic phase (block 1045), where biogas is generated and may berecirculated (block 1047) and/or injected into a second thermophilicstage (block 1065). Additionally, after the desired or appropriate dwelltime, feed stream from the first thermophilic stage is transferred to asecond thermophilic phase (block 1055); feed stream exiting the firstthermophilic phase will contain a decreased TSS percent as compared withthe feed stream that entered the first thermophilic phase. Thetemperature of the feed stream prior to transfer to the secondthermophilic phase is raised (block 1050) after which the feed stream isdigested (block 1065). During the second thermophilic digestion, biogasproduced may be recirculated (block 1067) or removed (block 1068) andfiltered to produce a first selected biogas, biogas A (block 1069). Inaddition, the remaining feed stream is digested for an appropriateand/or desired period and then cooled and transferred to a mesophilicstage (block 1070). In the mesophilic phase, additional biogas isproduced and removed (block 1080) and/or recirculated (block 1077).Biogas at this stage contains a large amount of methane, which may beselected for via a filter (block 1090).

FIGS. 11A and 11B illustrate a representative flow chart for producingone or more biogases, including methane, using two biomass digestersystems in parallel, depicted as A and B. In both systems, biomass isfed for use. In one embodiment, the feed stream is fed into a waterstream (blocks 1105, 1107), adjusted to a desired percent TSS—which maybe up to about 15% (block 1110) and up to about 5% (block 1112),aerobically hydrolyzed (blocks 1115, 1117), transferred to an acidifyingstage (blocks 1120, 1122) and acidified (blocks 1125, 1127). In otherembodiments, the feed stream is not adjusted in TSS and suitable forfurther processing (e.g., hydrolyzing, acidifying, etc.). Acidificationtimes for system A and system B need not be the same; however, bothsystems require a lower, more acidic pH. After the desired and/orappropriate dwell time, both acidified feed streams undergo andadjustment in pH and/or temperature (blocks 1130, 1132). In system A,the pH may be adjusted to between about 6.8 and about 7.2 and thetemperature may be about between about 125° and 135° F. (block 1130). Insystem B, the pH may be adjusted to between about 6.4 and 7.0 with atemperature may be about between about 135 and 158 ° F. (block 1132). Ineither or both systems, pH and/or temperature adjustments may occur inparallel or in series and prior to transfer to a first thermophilicphase (block 1135, 1137). In alternate embodiments, and in either orboth systems, temperature and/or pH may be adjusted duringmethanogenesis, such as at a thermophilic phase.

Referring now to FIG. 11B, thermophilic digestion is performed with bothsystems (blocks 1140, 1142) and biogas produced is recirculated (blocks1141, 1143) and/or removed (blocks 1170, 1147). Removed biogas isgenerally filtered and selected for one or more specified gases, such asbiogas A or biogas B (blocks 1175, 1149, respectively), which mayinclude methane and/or hydrogen. Alternatively or in addition, some orall of removed biogas from system A may be injected into thethermophilic phase of system B (block 1144). Feed stream after thethermophilic phase of either system is generally cooled and transferred(blocks 1150, 1152) to a next phase, which is the mesophilic phase. Inthe mesophilic phase, the feed stream is further digested (blocks 1155,1157) and biogas generated may be recirculated (blocks 1156, 1158)and/or removed (blocks 1160, 1162) and further filtered (blocks 1165,1167) to yield a select gas, such as methane. Alternatively or inaddition, all or a portion of biogas generated during mesophilicdigestion (blocks 1155, 1157) may be removed and injected (block 1159)back into the thermophilic phase of system B (block 1142).

The effluent stream from the thermophilic and/or mesophilic phases, richin nutrients and minerals, generally includes a large amount ofnitrogen, typically inorganic nitrogen in the form of ammonia. Nitrogenis one of the primary elements in soil biosupplements and fertilizers.To recycle liquid in the effluent (line 12, FIGS. 1A-1D), ammonia andother harmful elements must first be removed. Thus, it is beneficial toremove nitrogen from the effluent and reprocess it into biosupplementsand fertilizers.

Nitrogen, in the form of ammonia is generally removed from the effluentvia nitrification. Nitrification sequentially oxidizes ammonia to one ormore forms of nitrate. Nitrification can be accomplished by variousmethods known to one of skill in the relevant art. As described herein,denitrification closely follows nitrification to preserve nitrogen wheredesired. During denitrification, nitrates are converted to gaseousnitrogen via passage through a filter, such as a cation bed type filter(block 8, FIGS. 1A-1D). In one form, zeolites are used with or as acation bed filter.

Separation of solids from effluent generally includes transport of thefeed stream by pump and pipeline to a liquid-solid separation process(block 5, FIGS. 1A-1D), which is depicted schematically in one form andin more detail with FIG. 3. Referring now to FIG. 3, feed stream fromthe mesophilic phase (line 32A) and/or thermophilic phase (line 32B) arepassed through one or more dewatering systems (33 and 34). Suitabledewatering methods include a belt press, cyclone separator, screw press,resin bed, and other dewatering processes known to one skilled in theart that separate solids from a solid-liquid stream. In addition or asan alternative, solids may be separated by evaporation. The solids (38)are generally odorless and rich in nutrients such as nitrogen,phosphorous and other minerals. Such solids may be maintained in storageand/or may undergo further drying (39) using method known to thoseskilled in the relevant art. The effluent captured from the dewateringprocess is collected in an effluent line (35) and generally stored untiluse (37). Liquids obtained from a process described herein afterdewatering may be marked as a pathogen reduced organic liquid fertilizerbecause the liquid effluent of this process is high in nitrogen (in theform of ammonia) and other nutrients that make it an ideal organic ornatural fertilizer. The solids obtained from a process described hereinand after dewatering are generally classified as Class A Biosolids (asoutlined by the EPA). Part of the liquid effluent may also be recycled.The feed stream may be diverted in whole or in part, as production goalsdictate. Prior to re-use, liquid effluent must be further processed, asdepicted in blocks 7 and 8 of FIGS. 1A-1D, to remove nitrogen (generallyin the form of ammonia and other elements) by nitrification followed bydenitrification.

While alternative methods may be used (e.g., conventional methods, suchas reverse osmosis), a preferred method of nitrification as describedherein involves a biological contactor (block 7, FIGS. 1A-1D). Abiological contactor employs natural bacteria and/or microbes to performnitrification in the effluent. Suitable microbes include nitrosomonasand nitrobacter microbes. These and other microbes perform nitrificationin specifically aerated chambers within the biological contactor. Afterthe nitrification process is completed, the effluent is transported bypump and pipeline to a filter and/or other cation bed (block 8, FIGS.1A-1D) for denitrification. An example of an earth filter or cation bedis a zeolite that is able to accommodate a wide variety of cations,loosely held by the compound or filter and may be readily exchanged forothers in an appropriate solution. Many such zeolites, includingclinoptilolite, are thus re-usable as they are capable of recharging,such as by passing through a solution of salt water. In addition, or asan alternative, an earth filter when no longer suitable, may, itself, berecycled by adding it to the Class A Biosolids because spentfilters/cation beds will be high in nitrogen.

As discussed previously, criteria for classification of processedbiosolids is provided by the EPA (e.g., 40 C.F.R. §503). In addition, 40C.F.R. §503.32 (a)(3) describes alternatives to achieve Class A status.Applying said standards to the process and system described herein, oneresidence time at the thermophilic phase has been calculated to be at orabout 24 hours at or about 130-132° F. to provide pathogen reducedbiosolids when a feed stream has about a 7% solids content. Moreover,the liquid portion of the stream, also experiencing pathogen destructionfrom the thermophilic phase of the process, will provide a pathogenreduced liquid fertilizer at the completion of only a 24 hour residencetime. Pathogen reduction has been found to be significantly enhancedwith a sodium bicarbonate injection upon exiting the acidic phase (block2, FIGS. 1A-1D).

As is understood by one skilled in the relevant art, dwell time andtemperatures, particularly in the thermophilic and mesophilic phases, aswell as distribution and flow path of the feed stream will be adjustedto produce the desired quantity of biogas, fertilizer and/orbiosupplements. For example, a large portion of the feed stream may bediverted to a dewatering system after the thermophilic phase forrecovery of pathogen reduced organic fertilizer, while the remainingportion moves through the mesophilic phase to generate additionalbiogas, in addition to that generated during the thermophilic phase. Asan alternative, biogas production may be maintained at a level that isjust enough to provide for energy requirements for the digestion system.

As described herein, a multi-phase digestion system and process allowsfor an optimal microbial environment at each phase of the digestionprocess. Moreover, optimizing each phase means that the system andprocess herein provides for a significant reduction in dwell time ineach phase and increased biomass conversion efficiency as compared withalternative systems and processes. Additional benefits are that themulti-phase system and process allows for a reduction in reactor sizecapacity, while providing for the same or even more quantity of biogas,fertilizer and/or biosupplements. A reduced reactor volume and capacityreduces capital costs, lowers heating and mixing demands and overallenergy expenditures for heating and mixing of the feed stream duringoperational periods. In one form, a higher conversion efficiency asdescribed herein yields a greater amount of produced biogas, a cleanereffluent, a reduced volume of non-decomposed effluent solids, and anincreased volume of Class A Biosolids.

In one or more embodiments is disclosed a method of producing methanegas that includes stripping methane from other gases in a biogas mixturethat is obtained from either or both thermophilic and/or mesophilicphases.

In addition is disclosed herein a method of producing Class A Biosolidsthat includes a post-mesophilic stage of dewatering stage in which therecovered liquid is transferred to a liquid container or pipe and thepost-mesophilic stage products after dewatering include Class ABiosolids.

Still further is disclosed herein a method of producing pathogen reducedliquid fertilizer that includes performing mesophilic digestion on theacetic acid in solution, transferring the post-mesophilic stage effluentto a dewatering stage; and separating liquid from solid in thedewatering stage, whereby the liquid is obtained in the form of a liquidfertilizer.

Even further is disclosed herein a method of recycling water in abiomass digestion process that includes transferring post-mesophilicstage effluent to a dewatering stage, separating liquid from solid inthe dewatering stage, transferring the separated liquid to a biologicalcontactor, filtering the liquid through one or more times (e,g., firstwith a biological contactor and after with an earth filter) andre-entering the filtered water into an initial phase of the biomassdigestion process.

Still further is provided herein a system for generating a biogas,biosolids and pathogen reduced liquid fertilizer that includes aerobichydrolysis, anaerobic acidogenesis, at least one phase of anaerobicthermophilic methanogenesis, at least one phase of mesophilicmethanogenesis, a pH adjustment system to neutralize a feed stream priorto or during acidogenesis and/or thermophilic methanogenesis, at leastone heat exchanger in cooperation with acidogenesis, thermophilicmethanogenesis and/or mesophilic methanogenesis, a mixing device incooperation with acidogenesis, thermophilic methanogenesis and/ormesophilic methanogenesis, a gas lifting device in cooperation withthermophilic methanogenesis and/or mesophilic methanogenesis, a meansfor diverting at least a portion of a feed stream after thermophilicmethanogenesis and/or mesophilic methanogenesis, a dewatering system, abiogas treating system and optionally a liquid recycling system.

Described herein is a biomass digestion system that produces one or morebiofuels, including organic fertilizer and/or organic biosupplements,with a reduced amount of pathogens.

Enhancements provided and described herein include more manageable,efficient and controllable digestion processes and systems, each havingmore moderate and modifiable reactor conditions (e.g., TSS, pH and/ortemperature), which removes the potential for over-acidification andassists in isolating acidogenic microbes in order to manage their rapidand aggressive growth. In addition, efficient and timely biomassdigestion is obtained without the need for regular biomass supplements.

While specific alternatives to steps of the invention have beendescribed herein, additional alternatives not specifically disclosed butknown in the art are intended to fall within the scope of the invention.Thus, it is understood that other applications of the present inventionwill be apparent to those skilled in the art upon reading the describedembodiment and after consideration of the appended claims.

What is claimed is:
 1. A method for digesting a biomass, the methodcomprising: processing at least a portion of the biomass in a first unitto undergo a first digestion, wherein the first digestion is performedat a first temperature; processing at least another portion of thebiomass in a second unit, wherein the at least another portion of thebiomass transferred from the first unit to the second unit, wherein theat least another portion of the biomass in the second unit undergoes asecond digestion, wherein the second digestion is performed at a secondtemperature that is higher than the first temperature; processing atleast a further portion of the biomass in at least one third unit,wherein the at least further portion of the biomass is transferred fromthe second unit to the at least one third unit, wherein in the at leastone third unit the processing includes a third digestion, wherein thethird digestion is performed at a third temperature that is higher thaneither the first temperature or the second temperature; diverting atleast a portion of feedstream from the at least one third unit afterundergoing the third digestion, wherein diverting provides a bioproductsuitable as one or more of a fuel, supplement, fertilizer and gas. 2.The method of claim 1, wherein the first unit digestion is a hydrolysisreaction performed under aerobic conditions.
 3. The method of claim 1,wherein the second unit digestion is an acidification reaction performedunder anaerobic conditions.
 4. The method of claim 1, wherein the atleast one third unit digestion is a thermophilic reaction performedunder anaerobic conditions.
 5. The method of claim 1, wherein the firsttemperature is up to about 85 degrees Fahrenheit.
 6. The method of claim1, wherein the second temperature is greater than 85 degrees Fahrenheitand less than about 100 degrees Fahrenheit.
 7. The method of claim 1,wherein the third temperature is greater than 100 degrees Fahrenheit andless than about 160 degrees Fahrenheit.
 8. The method of claim 1 furthercomprising processing a still further portion of the biomass from the atleast one third unit to a fourth unit, wherein the still further portionof the biomass in the fourth unit undergoes a fourth digestion, whereinthe fourth digestion is performed at a temperature that is at or nearthe second temperature.
 9. The method of claim 1, wherein at least aportion of the bioproduct is diverted back into the system.
 10. Themethod of claim 1, wherein the biomass has a solids content of up toabout 15% when processed in the first unit.
 11. The method of claim 1processing in a fourth unit, wherein feed stream from the fourth unithas a portion of which is diverted for providing the bioproduct.
 12. Asystem for digesting a biomass, the system comprising a first unit forprocessing at least a portion of the biomass in a first digestion,wherein the first digestion is performed at a first temperature; asecond unit for processing at least some of the at least portion of thebiomass in a second digestion, wherein the second digestion is performedat a second temperature that is higher than the first temperature; atleast one third unit for processing a further portion of the biomass ina third digestion, wherein the third digestion is performed at a thirdtemperature that is higher than either the first temperature or thesecond temperature; a diversion unit for transferring at least a portionof feed stream from the at least one third unit to provides a bioproductsuitable as one or more of a fuel, supplement, fertilizer and gas. 13.The system of claim 12 further comprising a fourth unit for processingat least some output from the at least one third digestion, wherein thetemperature in the fourth unit is at or near a temperature of the secondunit.
 14. The system of claim 12 further comprising a second diversionunit for diverting some of the feed stream to a dewatering system,wherein the dewatering system separates solids from liquid in thediverted feed stream.
 15. The system of claim 12 further comprising atreating unit for treating the biogas.
 16. The system of claim 12further comprising a mixing system for circulating fluid in any one ofthe second unit and the at least one third unit.
 17. The system of claim12 further comprising a system for monitoring and adjusting oxygenlevels in the system.
 18. The system of claim 12 further comprising atleast one unit for modifying temperature of a portion of the system. 19.The system of claim 12 further comprising a pH adjustment system locatedbetween one or more of the first unit, the second unit, and the thirdunit.
 20. A composition obtained from the system of claim 12.